the capacity of existing lines, through the high speed and the higher energy density of silicon.
The high speed production comes from the tabless cell construction. Rather than using tabs top and bottom, the substrate of the ‘jelly roll’ that holds the anode, electrolyte and cathode has copper edges that are laser patterned. These fold over to produce the connections top and bottom. This avoids having to stop and start the line to insert the tabs
Using silicon provides higher energy density but suffers from cracking. “Silicon stores 9x more lithium than graphite but expands 4x when fully charged,” said Baglino. “Current approaches use engineered silicon materials and don’t scale – what we are proposing is a step change in capability and cost. We use the base silicon, which costs $1.2/kWh, and stabilise the surface with an elastic ion-conducting polymer coating, then use a highly elastic binder.”
Tesla is also mining its own lithium in Nevada using a saline process, and will build a cathode plant nearby. This will build cathodes with no cobalt with a variety of other materials such as iron and manganese that it already uses. Cutting out cobalt avoids sustainability and ethical production issues.
“This uses metal powder directly, eliminates billions in battery grade nickel production, with simpler mining and simpler recycling,” said Baglino. “We want to make sure we are not constrained by nickel supply but we need a three tier approach with iron [for stationary storage], Nickel Manganese [for mid range vehicles], then high nickel for long range for the cybertruck and the semi,” said Musk.
The answer to how Tesla addresses the swelling of the silicon may well come from the packaging of the cell which will be used as part of the structure of the vehicle, rather than in a separate